The present invention relates to a filter circuit for removing noise of a high frequency component in a magnetron for an electromagnetic range or microwave oven, and more particularly to a choke coil apparatus having an improved ferrite core which can restrain the increase in temperature of a choke coil.
A conventional magnetron for an electromagnetic range comprises an oscillator 10 for generating an electromagnetic wave signal of high frequency, and a filter circuit 30 connected between the oscillator 10 and a power source (not shown) for restraning the transmission to the power source of the high frequency signal generated in the oscillator 10, as shown in FIG. 1.
The oscillator 10 comprises a cylindrical anode 13 installed in upper and lower yokes 11 and 12, and a filament 14 installed on a central axis of the anode 13. A plurality of vanes 15 extended toward the filament 14 from the inner circumferential surface of the anode 13 are radially installed in the inner circumferential surface of the anode 13. Further, a plurality of cooling pins 16 extended from the outer circumferential surface of the anode 13 to the inner circumferential surface of the lower yoke 12 are installed in the outer circumferential surface of the anode 13. The cooling pins 16 externally emit the heat in the anode 13 by a thermion generated in the filament 14. Furthermore, the magnetic poles 17 and 18 extended toward the upper and lower ends of the filament 14 are respectively installed in the upper and lower ends of the anode 13. The oscillator 10 comprises permanent magnets 19 and 20 installed in the upper and lower portions of the magnetic poles 17 and 18, respectively, a center lead 21 extended from the upper end of the filament 14 to the filter circuit 30, and a side lead 22 extended from the lower end of the filament 14 to the filter circuit 30. The center lead 21 and the side lead 22 transmit to the filament 14 the operating voltage supplied via the filter circuit 30 from the external power source.
The filter circuit 30 comprises a filter box 31 and a lead through capacitor 32 installed in the side wall of the filter box 31 so as to pass through the side wall of the filter box 31, as shown in FIGS. 1 and 2. The capacitor 32 comprises first and second connecting terminals formed on the outside exposed portion of the filter box 31 for receiving a power source, and third and fourth connecting terminals formed on the inside portion of the filter box 31. The third and fourth connecting terminals of the capacitor 32 are respectively connected to the right ends of the choke coils 33 and 35. The center lead 21 and the side lead 22 are respectively connected to the other ends of the choke coils 33 and 35. Further, ferrite cores 34 and 36 are respectively inserted into the choke coils 33 and 35. The ferrite cores 34 and 36 are in the form of circular bars, as shown in FIG. 3.
The magnetron formed as described above operates as follows. The electron generated in the filament 14 is rotated by the magnetic field of the permanent magnets positioned on the upper and lower portions of the magnetic poles and moved to the anode 13. At this time, the electrons which are being moved form several rotating electron poles to allow the anode 13 to perform a very high frequency oscillation. The very high frequency components generated by the anode 13 are supplied to the choke coils 33 and 35 of the filter circuit 30 through a filament 14, a center lead 21, and a side lead 22. The very high frequency components supplied to the choke coils 33 and 35 is removed by the lead through capacitor 32 forming a low-pass filter together with the choke coils 33 and 35, so that it is not transmitted to the power source connected to the first and second connecting terminals of the lead through capacitor 32.
However, as the filament 14 is heated, the choke coils 33 and 35 are heated by the heat generated in the filament 14 and supplied through the center and side leads 21 and 22. Accordingly, there is a problem in that the choke coils 33 and 35 burn or the ferrite cores 34 and 36 are broken, due to the heating of the choke coils 33 and 35.